The three-phase choke with common-mode rejection serves as a standard filter choke. The fourth leg is used in this case for common-mode rejection.
Advantages
- Compact contruction compared to single-phase inductors
- One part instead of 3x single phase and therefore a significant price advantage
- Lower power losses as a single choke
The magnetic coupling of three phase filter chokes poses the challange at complex filter systems. Therefore, depending on the topology of power electronics, single-phase chokes will be applied.
If the currents are asymmetric, the inductances of the conventional three-phase chokes do not act in the same way as the one-phase winding goods; therefore the magnetic flows cannot be compensated and this causes a heating in the iron. If all currents of all three phases flow in the same direction at the same time, the three-phase choke only operates with its leakage inductance.
An alternative to the one-phase chokes are four-and five-leg chokes; developed by Schmidbauer! Another advantage: asymmetric load of the phases is possible.
